The present invention relates to a rod lens and an endoscope comprising at least one such rod lens.
Rod lenses per se are known and are for example used by the applicant under the designation “Hopkins Optics” in rigid endoscopes.
Rod lenses in general consist of a cylindrical body made from glass whereby the opposite circular ends are machined in order to form optical elements. The length of their body is usually many times bigger than their diameter.
Rod lenses have got the advantage that they conduct light for example in an endoscope with a higher efficiency than can be achieved with conventional plate-shaped lenses between which relatively large pockets of air exist.
Rod lenses made of glass have got the disadvantage, though, that they always form rigid bodies and cannot be used in flexible endoscopes. Therefore, in general, bundles of fiber optic picture guides are used in flexible endoscopes. Such bundles of fiber optic picture guides have got the disadvantage that they create a pixelated picture which reduces the precision of the representation notably.
Rod lenses made from glass further have got the disadvantage that they are made from a brittle material. During their daily use for example in an optical system of an endoscope, they will be dropped every now and then, leading to splinters coming off or even to the breakage of the rod lens. Such damage renders the optical system unusable. In such cases usually the complete optical system must be replaced.
In order to compensate for those disadvantages of rod lenses made of glass, flexible liquid filled rod lenses have been developed.
One example for such a flexible rod lens is known from U.S. Pat. No. 5,892,625. Such a rod lens comprises a tubular body which is tightly sealed on both ends by closing elements. Between those closing elements there is disposed a transparent fluid such as water or an optical fluid. In this way rod lenses are created which show at least some degree of flexibility. It has often proven difficult though to adjust such rod lenses to the desired optical characteristics.